Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $67.92   8.799%   $73.8963   $73.90   $73.90   $73.90  
  Purchase #2 $214.52   6.236%   $227.8975   $227.90   $227.90   $227.90  
  Purchase #3 $22.97   9.199%   $25.083   $25.08   $25.10   $25.10  
  Purchase #4 $127.36   4.827%   $133.5077   $133.51   $133.50   $133.50  
  Purchase #5 $181.71   6.350%   $193.2486   $193.25   $193.25   $193.20  
  Purchase #6 $222.42   12.545%   $250.3226   $250.32   $250.30   $250.30  
  Purchase #7 $233.57   11.458%   $260.3325   $260.33   $260.35   $260.30  
  7 purchase totals = $1,070.47       $1,164.2882   $1,164.29   $1,164.30   $1,164.20